Magnetoresistance of manganite thin films induced by reaction with substrate

Enhanced low-field magnetoresistance (MR) of polycrystalline lanthanum stro ntium manganite thin films is demonstrated using an approach in which effec tive barriers are formed by the heat-treatment induced reaction with an ins ulating substrate. The heat treatment induces two chemically different proc esses in the film, i.e., grain growth and chemically reactive penetration. In the former process, the MR decreases due to reduction of the number of g rain boundaries, while in the latter the penetration of an insulating subst rate and reacted materials forms effective barriers for the electron tunnel ing between ferromagnetic grains. The formation of effective barriers cause s a factor of 3 larger MR than as-prepared films. These results suggest tha t the MR can be prospectively controlled in this fashion. (C) 2001 American Institute of Physics.